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WaterDR · 09-27-2004, 09:21 AM

What a GREAT question! Wonderful lesson for so many to learn.

Plugs foul when the temperature in the combustion chamber does not get hot enough. This can be caused by using too high of an octane OR by using the wrong plugs for the application.

Spark plugs serve two purposes:

1 - They make spark and thus ignition
2 - They cool the combustion chamber.

Colder plugs, take more heat away then hotter plugs. Using colder plugs prevent "pre-ignition" but lead to fouling. As a rule, you should always use the coldest possible plugs w/o having fouling problems.

Cars with turbos, s/c, and nitrous require colder plugs due to the more fuel and higher compression thus more heat which tends to cause pre-ignition. Pre-ignition is when you get combustion BEFORE spark. Factors that lead to this are load on motor, temp of motor, ambient temp, using wrong octane fuel (too low).

ALWAYS USE THE FUEL WITH THE RECOMENDED OCTANE RATING FOR YOUR CAR!!!!!

Lower octane fuel burns faster and resists knock (pre-ignition) not as well as higher octane. The higher the octane fuel that you use, the slower it burns and the more it resists knock. To take advantage of higher octane fuel, you have to either increase compresion (which makes the fuel burn faster) and/or increase timing advance. Increasing TA makes the spark happen sooner which gives the slower burning fuel more time to burn.

In your case, by using 93 octane, you are not burning all the fuel and are ending up with fouled plugs and thus loosing performance. Your car will have more hp and fuel economy using 87 octane!

By having a chip or a programmer, you can have your timing advanced so that you can use higher octane fuel. I have an 87 octane program and a 93 octane program for my car. The difference is very noticable in power when driving with the 93 octane program and 93 octane fuel.

NEVER! use fuel that is too low of a grade! You merely fouled your plugs by using too high a grade, but using too low a grade can destroy an engine quickly.

Ask you service manager if he recomends using Sea Foam or similar product to clean your heads. You need to find out if you simply had fouled plugs or if the combustion changers are all fouled.

Using a chip/programmer will void your warrenty BTW. Though, if you use a programmer, you can have the stock tune re-installed before service work and they will never know it was ever there. If warrenty is a big concern for you, you may want to consider staying away from one.

09-27-2004, 09:21 AM	#2 (permalink)
WaterDR Administrator Join Date: Sep 2004 Posts: 6,366	What a GREAT question! Wonderful lesson for so many to learn. Plugs foul when the temperature in the combustion chamber does not get hot enough. This can be caused by using too high of an octane OR by using the wrong plugs for the application. Spark plugs serve two purposes: 1 - They make spark and thus ignition 2 - They cool the combustion chamber. Colder plugs, take more heat away then hotter plugs. Using colder plugs prevent "pre-ignition" but lead to fouling. As a rule, you should always use the coldest possible plugs w/o having fouling problems. Cars with turbos, s/c, and nitrous require colder plugs due to the more fuel and higher compression thus more heat which tends to cause pre-ignition. Pre-ignition is when you get combustion BEFORE spark. Factors that lead to this are load on motor, temp of motor, ambient temp, using wrong octane fuel (too low). ALWAYS USE THE FUEL WITH THE RECOMENDED OCTANE RATING FOR YOUR CAR!!!!! Lower octane fuel burns faster and resists knock (pre-ignition) not as well as higher octane. The higher the octane fuel that you use, the slower it burns and the more it resists knock. To take advantage of higher octane fuel, you have to either increase compresion (which makes the fuel burn faster) and/or increase timing advance. Increasing TA makes the spark happen sooner which gives the slower burning fuel more time to burn. In your case, by using 93 octane, you are not burning all the fuel and are ending up with fouled plugs and thus loosing performance. Your car will have more hp and fuel economy using 87 octane! By having a chip or a programmer, you can have your timing advanced so that you can use higher octane fuel. I have an 87 octane program and a 93 octane program for my car. The difference is very noticable in power when driving with the 93 octane program and 93 octane fuel. NEVER! use fuel that is too low of a grade! You merely fouled your plugs by using too high a grade, but using too low a grade can destroy an engine quickly. Ask you service manager if he recomends using Sea Foam or similar product to clean your heads. You need to find out if you simply had fouled plugs or if the combustion changers are all fouled. Using a chip/programmer will void your warrenty BTW. Though, if you use a programmer, you can have the stock tune re-installed before service work and they will never know it was ever there. If warrenty is a big concern for you, you may want to consider staying away from one. __________________ Black 2000 GT Vert: Novi-2000 with Intercooler (375rwhp @ 9 psi); Tune by Kauffmans; Roush 380R Body kit; Steeda Subframes; Steeda Strut Tower Support; Deep Dish Bullets; FRPP 4:10's; SCT 4 Position Chip with four custom tunes; Steeda CAI; C&L Pleum; BBK 75 TB; SLP Loudmouth; SLP Catted X-Pipe; Bullitt Suspension; UPR Conrol Arms; Focus Fuel Pump My Car My Email